How to fit a Fresnel Prism

Introduction

This leaflet has been produced for patients who have been given a Fresnel prism to fit and trial at home. Fresnel prisms are made of a flexible plastic which, once fitted to a pair of glasses, can alleviate horizontal and/or vertical double vision.

These prisms will not add any weight to your glasses, but you may notice some blur to your vision in the eye it is placed in front of which should begin to subside as you adjust to it.

Instructions

(To be filled by the clinician)

Prism strength:

Fitted to the lens of glasses:

Orientation of prism:

Note: If you wear reading glasses, we advise you wear these whilst fitting the prism to your distance glasses. If you are fitting a prism to your readers, you might need to ask someone to help you with this process.

1. Wash your hands and dry them well, then remove the prism from the packaging. The prism has two sides: a smooth side which will stick to the inside of your glasses lens, and a ridged side that will face towards your eye once fitted.

2. Remove your glasses, and place the prism smooth side down on the inside of the
glasses lens in the correct orientation and on the correct glasses lens (specified in the
box on page 1 which has been filled by your clinician).

3. Adjust the prism as required to get the correct position – this is very important as the
prism will only work if it is in the right orientation. Please see the below descriptions
and images for reference to ensure the prism is fitted in the correct orientation (the red
circles on the images highlight the position of the prism base).

4. Ensure the lines on the prism are completely perpendicular/straight when you place
the prism against the inside of your lens.

5. Carefully cut the prism out using a pair of scissors to fit the lens. You can trim any
excess later but cannot add back any prism that has been cut off

6. Check whether the prism fits on to the lens. If there is any overlap on to the frame,
continue trimming it down until the prism fits within the lens frame.

7. Once the prism has been cut to size, it can be fitted. Ensure you clean the glasses
as normal, then place a pool of water on the inside of the glasses lens. Gently place
the prism on to the lens with the smooth side down.
8. Squeeze out any excess water and air bubbles and dry with a tissue/cloth.

Tips for applying your prism

• Try to ensure the prism does not overlap the frame. If it does, it can cause it to peel off the lens meaning dirt and debris can gather under the prism.
• Do not refit the prism too often as the edges of the prism will curl upwards and it will not lie flat on the surface of your glasses lens.
• To clean the prism, use simple soap and water – lens wipes can damage and degrade the prism.
• You can also use an old soft toothbrush to gently clean the grooves of the prism of any dust or debris in the direction of the prism’s grooves.

My Chart

We would encourage you to sign up for MyChart. This is the electronic patient portal at Cambridge University Hospitals that enables patients to securely access parts of their health record held within the hospital’s electronic patient record system (Epic). It is available via your home computer or mobile device

More information is available on our website: My Chart

Contacts/Further information

Please contact the Orthoptic Department on 01223 216528 or via email if you have any queries between 08:30 to 16:45, Monday to Friday (we have an answer machine available 24 hours a day which is checked on a daily basis).